The present invention relates generally to diaphragm assembly interstage packing seals for steam turbines and particularly relates to segmented packing seals mounted on inner hooks of diaphragm assemblies and having spline seals for sealing the gap between the circumferentially adjacent endfaces.
A steam turbine has multiple stages. Each stage comprises a plurality of circumferentially spaced buckets about the turbine rotor and a plurality of nozzles forming part of diaphragm assemblies affixed to the stationary casing of the turbine. The nozzles and buckets are axially spaced from one another and disposed in the steam flow path. The diaphragm assemblies include inner hooks having dovetail-shaped grooves forming an annular groove for receiving interstage packing seals. The packing seals are mounted in the annular groove and carry axially spaced labyrinth teeth for sealing against the rotor. The packing seals are formed from arcuate segments disposed in the dovetail-shaped groove of the diaphragm assembly.
With steam turbine design, it is critical to minimize or eliminate any leakage paths within the turbine flow path and secondary leakage circuits. Because the packing seal segments are movable radially relative to the rotor, gaps appear between the endfaces of the segments and define steam leakage paths. These endface gaps can be sufficiently large to produce leakage between the high and low pressure regions on opposite sides of the diaphragm nozzles which can cause significant efficiency loss and loss of potential revenue for a power producer utilizing the steam turbine. The gap between adjacent seal segments is a result of the radial movement of the seal segments, machining tolerances, as well as thermal responses to the high temperature conditions during operation of the turbine. Accordingly, there is a need for seals in the endface gaps between packing seal segments in steam turbines to minimize or preclude steam leakage flows through the endface gaps.